Hey Helen,
Small talk rules change with the local mix of density, privacy norms, and how often strangers have to share space. In places where people are crammed together daily, the rule is often polite invisibility to preserve privacy, like eyes down on a crowded metro. In smaller or slower places, acknowledging each other signals goodwill and safety, so quick chats are expected while waiting. Layer on culture around directness versus indirectness and you get very different default vibes even between neighborhoods in the same city.
To read it fast, run a three step scan the first day. Watch two or three interactions in a line and note volume, eye contact, and whether replies include a return question. Then try a low commitment probe that gives them an easy out, like Is this the line for gate B or do I need to check in first, said with a half smile and then you look back at the sign. If they give a one word answer, keep facing forward and end with Thanks, have a good one. If they turn their shoulders toward you and add a comment or a question back, you can do one more beat about the shared situation and stop after 30 to 60 seconds unless they keep it going. Distance and posture matter too, about an arm's length in most Western settings, closer only when the space forces it and you avoid direct eye contact on packed transport. These tiny tests keep you from overcommitting and they calibrate fast to places where Tube rules dominate versus places where a checkout line feels like a tiny neighborhood.
